How to structure Android app navigation with many levels?I should have made it clear that this app is a phone app, and will 99% of the time be used in portrait. Sorry for not making that clear. I'm not sure I understand your last paragraph. If you're suggesting using two rows of tabs and the lower set as sub-tabs, I'd be concerned people wouldn't realise they were a level down.

Where to put OK/Cancel on an Android activity form?If the buttons do not scroll, then this layout probably won't work on a very small screen device, as the mandatory items will take up all the space. Even if there is a small letterbox space for the scrolling content, it will be too small. I'm not keen to allow the ActionBar to scroll off the screen. Of course once Ice Cream Sandwich arrived and we have Honeycomb UI on phones, the ActionBar may become appropriate for context-sensitive options. I'm not convinced any of the options I've laid out above are that great.